import java.util.*;
public class E {
   public static void main(String args[]) {
     Stack<Character> mystack1=new Stack<Character>();
     Stack<Character> mystack2=new Stack<Character>();
    StringBuffer bu=new StringBuffer();
    for(char c='A';c<='D';c++) {
       mystack1.push(new Character(c));
    }
    while(!(mystack1.empty())) {
      Character temp=mystack1.pop();
      mystack2.push(temp);
    }
    while(!(mystack2.empty())) {
      Character temp=mystack2.pop();
      bu.append(temp.charValue());
    }
    System.out.println(bu);
   }
}
